The present invention relates to steering columns for a variety of vehicles or vessels and more particularly relates to such columns which have a telescoping feature.
Various telescoping steering columns are available today in a variety of vehicles. The basic structure of a telescoping steering column commonly includes a tube portion connected with a steering gear and a shaft portion slidably received in the tube. One end of the shaft will project from the tube and couple with a steering wheel or the like. Also, rotational torque must be transmitted between the shaft and the tube. This torque transmission is commonly accomplished by machining cooperating splines on the outer surface of the shaft and the inner surface of the tube. However, this is an expensive machining operation and makes the telescoping steering column a costly option.
A modification of the spline approach is to form each of the shaft and the tube with cooperating cross-sectional shapes which will preclude rotation between the shaft and the tube and allow sliding of the shaft relative to the tube. These shapes commonly take the form of a polygon or modified polygon. However, this may again require expensive machining of the parts.
Another modification or alternative to the spline approach is to mill a keyway into one or both of the shaft and the tube and use a key extending between the shaft and the tube in the keyway. Clearly, this approach also requires machining to form the keyway and the key, which may be a separate part or a projection from one of the shaft and tube.
Another consideration in the design of a telescoping steering column is control of rotational lash. A certain tolerance must be allowed between the shaft and the tube to provide sufficient clearance for these parts to slide freely, one in the other. However, the tolerances which make the shaft and tube free sliding also introduce rotational lash or play between these components. The presence of lash emphasizes the need for close tolerance machining of the shaft and tube. Conversely, additional devices to take up the lash between coarsely formed shafts and tubes may be added to the telescoping steering column to hold the rotational lash within acceptable limits. However, these lash control devices also require machined components and add further complexity to the column.
Other components which are commonly required in a telescoping steering column are stops to define the range of axial travel of the telescoping motion. These stops are required for a number of reasons which may include keeping the column assembled, rather than allowing a user to simply pull the shaft out of the tube. Also, the splining or keying which transmits torque between the shaft and the column may not extend along the entire length of each of the shaft and tube so that stops are required to limit the steering column from being retracted or extended beyond the engagement of the splining or keying.
Taken all together, the various requirements for a properly functioning telescoping steering column commonly requires a considerable number of specially formed or machined parts to be assembled. Thus, the typical telescoping steering column may be a complex and costly device.